1. Field of the Invention
This invention relates to a magnetic core and a method of manufacturing the same. More particularly, the invention relates to a high power pulse magnetic core, for example, a saturable magnetic core for use as an electric pulse source for laser or as an induction core for a linear accelerator, and a method of manufacturing the same.
2. Description of the Related Art
A high power pulse magnetic core, such as an induction core for a linear accelerator, applies voltage generated in the secondary gap to accelerate an electron beam through the center of the core.
A magnetic pulse compressor is used in a pulse power source for generating a laser. The pulse compressor can generate high power and operates at high voltage. The pulse compressor compresses a relatively wide pulse generated in the power source to a narrow, high power or spiked pulse and uses the saturation phenomenon of the magnetic core.
Consequently, magnetic cores for these high power pulse devices are made of cobalt alloy amorphous films or ferroalloy amorphous films and polyester films or polyimide films, which are layered alternately. The cobalt alloy amorphous and ferroalloy amorphous films are characterized as having high saturated magnetic flux density, a large squareness ratio of magnetization curve, a low coercive force and a low iron loss. Also, the polyester films and polyimide films have high insulating characteristics.
However, problems are associated with magnetic cores of cobalt alloy amorphous films. One of take problems is that such magnetic core has a low saturated magnetic flux density as compared to magnetic cores of ferroalloy amorphous films. Another problem is the high cost of cobalt alloy materials.
On the other hand, a magnetic core comprising ferroalloy amorphous films and polyester films or polyimide films, the latter being inserted between the amorphous films, has characteristics of high saturated magnetic flux density, and the cost of the ferroalloy materials is low. However, when the polyester films are used as insulators between the amorphous films, the core cannot take heat treatment (about 400.degree. C.) that is needed to make up the magnetic characteristics because the heat resisting temperature of the polyester film is about 200.degree. C. As a result, the magnetic core lacks high magnetic characteristics. As a solution to this problem, before stacking the alloy and polyester films and winding the stacked films into the core, the amorphous alloy films only are heat-treated. But in this way, the magnetic characteristics are deteriorated because of stress acting on the alloy films when they are wound into coil shaped cores with the polyester films.
When the polyimide films are used as insulators, the magnetic core can be heat treated after stacking and winding because the polyimide film has a high heat resistance. However, the polyimide film is very expensive. Also, the polyimide films contract under heat treatment and contribute to stress in the amorphous films which, in turn, may result in deterioration of magnetic characteristics.
In a magnetic core made by the method mentioned above, the direct current coercive force is very high. Therefore, a large number of windings are required for reset or the size of the electric source capacity for reset must be large, especially in the case of high output pulse magnetic core. This is one of the major problems incurred in making the magnetic core industrially. Moreover, the magnetic core made by the method as mentioned above has a low total value of residual magnetic flux density and saturated magnetic flux density, that is, under 24 KG. Therefore, the shape of the magnetic core must be larger in size to obtain the required magnetic characteristics.
Conventionally, the amorphous alloy films are heat-treated between the temperature of 380.degree. C. and the temperature of crystallization. In this condition, structural relaxation is carried out at a rate of progress sufficient to keep the shape of the films. However, when the alloy films are wound alternately with high polymer films, the alloy films are stressed and the magnetic characteristics of the resulting core reduced.